Production of modulated waves



' Patented Nov. 16, 1926.

UNITED STATES PATENT OFFICE. RAYMOND A. HEISING, OE MILLBURN, JERSEY, ASSIGE'OR TO WESTERN ELEC- I TRIO COMPANY, INCOB PORA'I'ED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

\ PRODUCTION OF HOEUL ATED WAVES.

Application filed July 17, 1922. Serial No. 575,591.

The present invention relatesto the production of modulated waves, and more particularly to the production of high frequency oscillations modulated in accordance with 5 relatively low frequency signaling or control currents.

This invention is related. to the system and method of modulation disclosed in my prior Patent, No. l,4t2,1 47 dated January 16,

o In the specific arrangement disclosed in my.

prior application referred to, two separate electron discharge tubes of the audion type have their plates or anodes connected together and their filaments or cathodes connected W5 together,*while between the common plate connection and; the common filament connection, there is'a path including a high impedance and a source of space discharge current for both tubes. Variations in,-the space current of one tube produce. corresponding variations in the space current of the other tube," said impedance preventing these variations from passin through it. By arranging one of said tu es to supply high frequency oscillations to any desired system, and controlling the space current of the other tube directly by signals, for example, the corresponding variations in the high-frequency tube cause the supplied a waves to be modulated in accordance with the signals impressed on the other tube.

Experience has shown that in some cases it is advanta eous to use a difierent anode voltage for t e tube or device which fur- 5 nishes the high frequency oscillations from that used for the tube or device upon which the signals are impressed. Particularly if discharge tubes of the same type and dimensions are used for both purposes it has been it found that to secure the most effective degree of modulation of the high frequency wave, a higher anode voltage should be used for the tube upon which the signals are impressed than for that, which supplies the high frequency oscillations.

The present invention enables these advantages to be attained in that it provides a modulating arrangement in which separate sources of discharge current are employed for the separate discharge devices respectively from which the modulated oscillations are supplied and upon which the signals are impressed.

In the arrangement according to the invention to be described more fully hereinafter, the space current circuits of a plurality of discharge devices upon certain of which the signal variations are impressed and from other of which the modulated oscillations are supplied, are associated with each other,

and two separate sources of discharge current are provided forthe devices which fulfill these two functions. Thetwo space current circuits are connected b pathsof low impedance for signaling variations. When signals are being transmitted, variations in the spacecurrent of the first circuit set up a signal wave electromotive force in an inductance in that circuit, and this electromotive force is accordingly; applied, to. the

other space current circuit to cause a complemen'tal current variation therein relat ve to thevariatron in the first circuit and to effect corresponding variations in amplitude ting circuits embodying the invention, and

.Fig. 4 shows an alternative arrangement capable of use in the circuits of the other figures.

In Fig. 1 the transmission circuit 1, which is specifically shown as an antenna but which may equally well be any desired typeof.

circuit such as a line, is supplied with carrier oscillations from the source 2, and the ampli tude of these oscillations is varied under circuit 4. The circuit 4 is specifically shown as a microphone circuit containing batvto the antenna 1.v Either or both the antenna and the plate" circuit may have pro vision for tuning,'as by the constants of. the antenna and by the condenser 10. By thus coupling the plate circuit 8 and the grid circuit 9 to the antenna, the tube 2 is made to generate sustained oscillations in the antenna for-transmission. If desired, amplification for the waves from the source 2 may be .provided before transmission, if the source 2 is of insufficient power. Other types of circuit connection may be used for causing the tube 2 to generate oscillations and supply them to the antenna, a number of suitable connections bein known in the art. Space current for t e oscillator 2 is supplied from the source 11 which may be a battery or a enerator of any suitable type. Included in the supply path a from source 11 is an impedance 12, the

action of which "will be explained: later.

. The discharge device 3, upon which the signaling variations from circuit 4 are impressed, has its space current supplied from-source 13,'and its supplg circuit also conditions.

includes the impedance 12. voltage of -source 13 may be the same as, or different from that of source 11, depending on the type. of tubes used and ossibly other When tubes 2 and 3 are of the same type and have the same anode-cathode impedance it has been foundadvantageousto make the voltage of, source 13 of the order of 25% 01-60% higher than that of source 11. It is advantageous to make the impedance of the coil 12 at the most sensitive signaling frequency (in the case of speech about 800 or 1000 cycles) greater than the plate-circuit impedance of the os cillator when it is. oscillating ata. steady. amplitude, although the circuit works well if the coil impedance is only about equal to the oscillator impedance. "By wa of example it may be stated that if the C- im-. pe ance between the cathode and anode of V the oscillator tube 2 when it is oscillating is 10,000 ohms, theimpedance of 12- for the most sensitive signal frequency, say 1000 cycles, is preferably the sanie. or' greater,

and in case this impedance of coil 12 is practically entirel inductive it may be 1.0

or 1.25 henry. owever, the im edance of 12 may also consist partly or argely of stated, the v ohmic resistance. The plate impedance of tube 3 underits operating conditions would in the case of the above values be about 7 000 ohms, on the assumption that it is the same type of tube as 2. These values are g1ven-byway of example only and are not' to be taken as limiting the invention. The high frequency choke 14 freely transmits current variations of signaling frequency but ofi'ers great opposition to the passage through it of variations of the frequency of oscillation of the source 2. The waves generated by .the source 2 are therefore prevented from being shunted through the tube 3 or any distributed capacity of choke 12 and its associated circuits and are confined principally to the circuits of the tube 2 and antenna 1. Blocking condenser 16 prevents the short-circuiting of battery 11 through] the inductance winding of circuit 8. The cathodes of tubes 2 and 3 may be provided with high frequency grounds, as

shown in U. S. Patent No- 1,388,450 to 001- pitts et al., dated :August 23, 1921. The

combination of resistance and capacity indicated at 19 is for the purpose of fixing the avera descri ed in my prior Patent No. 1,413,? 32, April 25, 1922. 4 i

In operation, continuous oscillations are produced in .the transmission circuit 1 by the well-known action of the tube 2.. So long as no sounds are-produced before the microphone 6, these oscillations continue with constant and unvarying amplitude,

since the circuit elements and the quantities 'which determine the steady operation of the source 2 remain unchanged. As described above, however, the plate circuits of the tubes 2 and 3 areinterlinked in such away that variations in the current through the tube 3, in accordance with speech for example, are accom anied by corresponding variations in the space current of the oscillator 2 and the amplitude of the oscillations produced in'the antenna 1 varies accordingly. Thus, as the impedance of tube 3 varies in accordance with sound waves, for example, inci-dent 'upon microphone 6, the current through the tube 3 from the source 13 is caused to vary and the choke 12 generates an electromotive force between the "points 17 and 18-of such direction as either to" add to or subtract from the voltage of potential of the grid in a manner sources 11 and 13. Thus a momentary increase in the impedance of tube 3 causes an impulse of increased space current in the oscillator tube 2, and a momentary decrease in impedance of the tube 3 causes a decrease in the space current of the tube 2. The sum of the space currents in the tubes 2 and 3 is from instant to instant substantially constant.

The circuit of Fig. 2 is identical with that of Fig. 1 except as regards the ground connection (and the difierence in this is immaterial) and the connection for supplying space current to the oscillator tube 2. In Fig. 2 the space current supply leads for the tube 2 are connected directly to opposite terminals of the blocking condenser 16, so that this condenser not only prevents short-circuit'ing the space current source 11 but acts as a high frequency shunt of prac tically zero impedance, on account of its relatively large size, across the tube 3 so that the carrier oscillations are confined to the circuits of. the generator 2. l Vith this arrangement the high frequency choke 14- is unnecessary and may be omitted. The condenser 16 of this figure, while large enough to transmit freely the high frcquency oscillations from source 2, is stillv sufiiciently small to ofier high impedance to currents of signal frequency so that they are caused to pass through the tube 2.

In Fig. 3 two choke impedances 20 and 21 are provided for the two space currentcircuits of the tubes 3 and 2, and the corresponding terminals of these chokes are joined by low impedance paths which might be constituted in any appropriate manner but are shown as comprising the condensers 22 and 23 respectively. I If instead of these condensers, conductance paths of low impedance were used the circuit would reduce to substantially that of Fig. 1 with two chokes in parallel in place of the one choke 12. This type of connection admits of both filamentsof tubes 2 and 3 being grounded directly,

and also permits a single direct current source or heating current to be used for bot-h filaments, as shown.

The operation of the circuit of Fig. 3 may be explained similarly to that described above for the circuit of Fig. l. The condensers 22 and 23'permit the free passage of current variations of the signaling frequencyl A change in the current through the tube 3, and hence through the choke 20, causes the choke 20 to generate a momentary electromotive force between its terminals, and this is communicated by the condensers 22 and 23 to terminals of the choke 21 andto 'the tube 2 in parallel thereto. The choke 21 ofi'ers great opposition to a change in the current through it with the result that the electro motive force communicatedfroin the choke 20 is relieved by a change in the space current through the tube 2. The actual. space current through the tube 2 is therefore greater or'less depending on whether the super-- posed elect-romotive force "aids or opposes that of source 11. I 1 y In the case of each of the Figs. 1, 2 and 3, the tube two is shown and has been described as provided with circuits for causing it to generate the high frequency oscillations transmitted by the circuit 1. In each case,

however, a separate source of waves may be.

associated with the tube 2 for supplying the high frequency waves for transmission. One such arrangement is shown in Fig. 4, in which the source 25 is associated with the grid circuit of tube 2 through the transformer couplin 26. The arrangement of Fig. 4 maybe su stituted for that portion of any of the circuits of the other figures, lying to the right of the line ab. Suitable ground connection (not shown) to the cathode of tube. 2 may be made by a condenser such as 15, or conductively in casethe cathode of tube 3 is connected through a condenser to ground, as hereinbefore explained, or in case the type of circuit shown in Fig. 3 'is used. In this arrangement the tube 2 repeats, the waves furnished by the source 25, and preferably amplifies them. It

'alsocontrols the amplitude of the waves transmitted, due to changes in its space current caused by changes in impedance of the tube 3 as described in connection with the other figures. I

The invention is not to be construed as limited to the specific circuit arrangements that have been shown and described in detall, but only by the scope of the appended claims.

What is claimed is: 1

'1. A modulation system of the constant current type comprising electric discharge devices having cathodes, anodes and control electrodes, means for impressing carr er frequency oscillations on one of said dev ces, means for impressing modulating oscillations upon another of said devices, said two devices having such characteristics as to adapt them for different space current voltages whereby high modulation efliciency maybe obtained, separate space current sources con-.

nected respectively to said two devices and having electromotive forces suitable for the device to which they are respectively connected, and means for maintaining the sum of the space currents, of said two devicesefl'ectively constant at the frequencies of the ion modulating waves while permitting niodu- I latingfrequency variations of opposite sign in the individual space currents.

1 2. A .modulation system of current type comprising electric discharge devices each having a cathode, an anode and control electrode, means for controlling the space current of one of said devices by carrier frequency osc11lat1ons, means for conthe' constant trolling the space current of another of said devices by modulating oscillations, said two devices having such characteristics as to adapt them for different space current voltages wherebynhigh modulation efliciency may be obtained, separate space current sources connected respectively to said two devicesand having electromotive forces-suitable for the circuit; a separate source of space current for each of said tubes; means for supplying high frequency oscillations to the grid cirof the other cult of one of said tubes and relatively low frequency signalin waves to the 'grid circuit of the other 0 said tubes; high inductance means between said sources of space current and said anodes arranged with respect to said anode circuits for causing the variations of signaling frequency in the space discharge currents of said tubes to be substantially complemental to each other whereby the high frequency oscillations in said one tube are modulated in accordance with the signaling waves impressed on the other tube.

4. In combination, two electron dischar e devices, each having a cathode, an ano e and a grid, anode circuits and grid circuits therefor, a separate source of space currentfor each device connected between its cathode and anode, means in circuit with said plied to said anodes substantially constant as regards variations of signaling'frequency, means to supply signaling frequency variations to the grid circuit of one of said devices and high frequency oscillations to the grid circuit of the other device and connections for impressing signaling frequency variations from. the anode circuit of the first device upon the anode circuit of the second device formodulating the high frequency oscillations in accordance with signals.

5.- In combination, two electron discharge tubes, each having a cathode, an anode, a grid, an anode circuit and a grid circuit; means for impressing signaling variations on the grid circuit of one tube independent id circuit; means for impressingv sustain high frequency waves on the grid circuit of the other tube independent of the first grid circuit; separate sources of space current for said anodes and. means associating said-anode circuits for keeping the sum of the currents supplied to the two low anodes substantially constant as regards variations of signaling frequency. 1

6. In combination, an electron dischargespace current; means tomaintain constant as regards'variations of s gnalingfrequency the sumofflthecurrents" supplied from said sources of-current to said discharge tubes;

and means to vary the space current of said second discharge tube under control nf signals to be transmitted. I c

7. Incombination, a plurality of electron discharge devices each-having space discharge electrodes, a transmission circuit, connections for utilizing one of said devices to supply sustained high frequency oscillations to said transmission circuit, a source of discharge current'for said one device, a separate source of discharge current for another of said devices, means to vary the discharge current through said last-mentioned discharge device in. accordance with signals to be transmitted, and means to maintain the sum of the discharge currents supplied to said devices constant as regards variations of signaling frequency.

8. In combination, a plurality of electron discharge devices, circuits for supplying discharge current thereto, a transmission circuit, connections for utilizing one of said devices to supply high frequency oscillations to said transmission circuit, a source of discharge current for said one-device, a source of discharge current for another of said devices, means to vary the discharge current through said last-mentioned device in accordance with signals to be transmitted, and means interlinking the discharge current supply circuits of said devices for causing a sources for keeping the total current sup- -d ecrease or increase in the discharge current supplied to said first-mentioned device when an increase or decrease, respectively, occurs in the discharge current of the second-mentioned device.

9. In combination, .an electron discharge device, a source of discharge current for supplying said device, a'second electron d scharge device, a source of discharge current for supplying ,said second device, said sources being of respectively different voltage, connections for utilizing the first of said devices to transmit high frequency oscillations, means to vary the discharge current through the second device at a relatively low frequency rate compared with the fre-- quency of said high frequency oscillations,

and nieansfor causing the supply of discharge current to said first discharge device to vary in a manner substantially complemental to the variations in the discharge current through the second device, whereby frequency amplitude variations are produced in said high frequencyoscillations.

plying current from said source to said tube,

connections for utilizing said tube to transmit high frequency oscillations, a second discharge tube having a cathode and an anode, another source of discharge current and a circuit for supplying discharge current from said latter source to said second tube, means to impress signal waves on said second tube, a path connecting said anodes and capable of freely transmitting currents of signaling frequency, a path.

connecting said cathodes and capable .of freely transmitting currents of signaling frequency, each of said current supply circuits including a high inductance port-ion offering very great opposition to the passage through it of currents of signaling frequency whereby current variations of signal frequency in said second tube are caused to pass through said first tube and vary the amplitude of the high frequency oscillations transmitted.

12'. In combination two circuits, each of said circuits being composed in part of an electron discharge space and a source of space discharge current, inductance choking means associated with said circuits, said cir-. cuits having a connection with each other at each side of said means, and means individual to one of said circuits for producing Variations in the discharge current in said one circuit of a frequency too high to pass readily through said choking means, where by variations are produced in the discharge current of the other circuit.

13. In combination two circuits, each of said circuits including an electron discharge space and a source of discharge current individual thereto, means individual to one of said circuits for producing variations in the discharge current in said one circuit, said circuits having aconnection with each other at one side of said sources of discharge current and at vanother point, and inductance choking means included in said two circuits between said connections, of such high inductance as substantially to prevent the passage therethrough of said variations.

14. In a modulating circuit a plurality of electron discharge tubes, circuit arrangements for said tubes including means to impress signals" on certain of said tubes and means to use other of said tubes to supply carrier oscillations modulated in accort ance with said signals, said circuit arrangements also including a path, a portion of which at least is individual to the certain of said tubes upon which the signals are impressed, said portion including a source of space discharge current, said circuit arrangements also including a path a portion of which is individual to the other of said tubes, said portion including a source of space discharge current, and inductive choking means included between said sources of discharge current and the discharge spaces of said tubes, having an inductance of such I magnitude as substantially to prevent the passage through said choking means of current variations of the signaling frequency, said circuit arrangements also in-' cluding a path exclusive of said choking means and extending through the discharge spaces of said certain of said tubes and said other of said tubes in series.

15. The arrangement specified in claim i 14: in which said inductive choking means comprises two inductors and means whereby they are substantially in parallel with respect to current variations of the'signaling frequencybut individual, respectively, to said certain tubes and said other tubes as "regards unvarying current.

In witness whereof, I hereunto subscribe, my namethis 13th da of July, A. D. 1922. a

i RAYM ND A. HEISINGr. 

